This invention relates to the field of gas purification, and to the ultra-purification of bulk or matrix gases that are useful in the microelectronics manufacturing industry. More specifically, the invention relates to methods and materials for selectively removing trace hydride impurities and moisture from matrix hydride gases and inert or non-reactive gases.
As semiconductors become smaller and the devices using semiconductors become more sophisticated and therefore more demanding of the semiconductors, the perfectness property of semiconductors becomes an issue of great concern. The manufacture of semiconductors involves the use of reactive gases that are composed of various elements. In addition, manufacturing processes such as metal-organic chemical vapor deposition (MOCVD) and other related manufacturing techniques are used in the manufacture of semiconductors. In these processes the purity of the reactive gases plays a large part in determining the quality of the semiconductor product being manufactured, and in particular the electronic quality of the semiconductor product. Consequently, there is an increasing demand in the microelectronics industry for ultra-pure process gases. Thus, the ultra-purification of gases useful in microelectronics processes has experienced extensive technological effort and advances.
Existing methods of purifying gases used in manufacturing microelectronics devices are generally insufficient for meeting the need for ultra-pure gas. While parts-per-billion (ppb) levels of impurities were tolerable at one time, such levels are now regarded in many processes as too high. This technological effort is nourished by improvements in the analytical techniques that are used to detect impurities in gases. Presently, the ability exists to provide impurity detection limits that are in the ppt levels, for example by using Atmospheric Pressure Ion Mass Spectrometry (APIMS).
Group IIIB metals (e.g., gallium (Ga) and indium (In)) and group VB elements (e.g., phosphorus (P), arsenic (As), and nitrogen (N)) are of special importance in the manufacture of semiconductors in that they are constituents of the so-called Group III/V semiconductors. For example, arsine (AsH3), phosphine (PH3) and ammonia (NH3) are used in the manufacture of Group III/V semiconductors such as gallium arsenide (GaAs), indium phosphide (InP) and gallium nitride (GaN), respectively. Traces of foreign elements in these semiconductor materials are harmful, especially if the foreign elements are Group IVB elements (e.g., Si and Ge) and/or Group VIB elements (e.g., S and Se), which adversely contribute an acceptor effect or a donor effect to the semiconductor material. Unfortunately, trace impurities of Group IVB and VIB elements are very common in so called xe2x80x9cpure gasesxe2x80x9d. For example, phosphine and arsine may include traces of silane (SiH4), germane (GeH4), hydrogen sulfide (H2S) and hydrogen selenide (H2Se). In addition, trace quantities of oxygen (O2), oxides such as carbon monoxide (CO) and/or carbon dioxide (CO2), and oxides derived from phosphine and arsine (e.g., HxPyOz, and HxAsyOz, wherein x, y and z are small integer numbers) have also been detected in xe2x80x9cpure gases.xe2x80x9d Such impurities are also harmful in semiconductor processes.
Impurities in hydride gases used in the production of semiconductor devices, especially hydride-impurities of other elements, may originate from the hydride bulk gas itself, or from materials that are within gas handling and distribution devices such as gas containers, gas cylinders, gas valves and gas regulators, and even from gas lines that interconnect these devices.
U.S. Pat. No. 5,385,689 discloses a method of purifying semiconductor process gases using a scavenging composition that removes water, oxygen and other oxidants and Lewis acids from gas streams such as hydrogen, nitrogen, helium, neon, argon, krypton, and xenon, and Group IVA-VIA hydride gases such as silane (SiH4), germane (GeH4), ammonia (NH3), phosphine (PH3), arsine (AsH3), hydrogen sulfide (H2S), and hydrogen selenide (H2Se). The scavenging composition is formed by the deposition of a Group IA metal (Na, K, Rb, Cs, or mixtures or alloys thereof) onto an inert, macroreticulate polymer support, followed by pyrolysis at an elevated temperature.
Japanese Patent Application No. 4124001A2 describes a method of purifying arsine using an activated alumina gel. Nitrogen gas that has been heated to 110-200xc2x0 C. is used to activate a granular alumina gel. Unpurified arsine is brought into contact with the alumina gel, and the temperature is raised to remove impurities from the arsine. However, JP 4124001A2 specifically states that the alumina should not be heated to temperatures over 200xc2x0 C., stating that temperatures over 200xc2x0 C. will turn the alumina gel into a powder, thereby rendering the alumina incapable of purifying gases.
Nippon Sanso Corporation has developed an alumina catalyst called MN Purificator(trademark) (also called NSC NeoBead, NeoBead or NB) which selectively removes silane from arsine (Japanese Patent No. 2-246533; Takuya, et al., J. Cryst. Growth, 124: 272-277 (1992)). The mechanism whereby silane is removed from arsine by the MN Purificator(trademark) as the arsine passes through alumina is proposed to be a chemical reaction as shown in Equation 1.
SiH4+[Al(OH)]2xe2x86x92(AlO)2xe2x80x94SiH2+2H2xe2x80x83xe2x80x83(1)
Alumina such as the NeoBead material mentioned above is known to remove silane and hydrogen sulfide impurities from inert gas streams such as nitrogen and from the hydride gases arsine and phosphine. However the NeoBead material is ineffective in the elimination of traces of germane impurities from hydride and inert gas streams.
Watanabe, et al. (Journal of Materials Science: Materials in Electronics, 9:127-132 (1998)) describe the adsorption of B2H6 and H2Se on porous xcex3-alumina (gamma-alumina) and amorphous silica, and discusses the reactivity of hydrides (B2H6, PH3, AsH3, and H2Se) to alumina and silica in terms of the basicity of adsorbents and the proton affinity of hydrides.
Ikeda, et al. (Journal of Crystal Growth, 124:272-277 (1992)), describe the reduction of the H2O and SiH4 content of in AsH3 by treating the inner surface of an aluminum cylinder in order to form a clean and smooth oxide layer, and by developing a catalyst that selectively decomposes the SiH4.
A need remains in the art for an effective purifier apparatus and purification method for removing trace impurities from so-called pure gases, specifically the removal of trace hydride impurities from bulk or matrix hydride and non-reactive or inert gases. In particular, there is a need for the selective removal of trace quantities of hydride impurities of Group VB elements such as phosphorus (P) and arsenic (As) and Group IVB elements such as silicon (Si) and germanium (Ge) from hydride gases and non-reactive or inert gases. Such hydride impurities pose environmental and health hazards because of their extreme toxicity, and elimination of these hydrides from bulk and matrix gases is desirable down to the sub-ppm level
The present invention overcomes the deficiencies of prior art adsorption-based gas purification systems that seek to remove impurities from hydride gases. The invention provides a gas purification system that is especially adapted for, but is not limited to, use in the purification of gases that are thereafter used in the manufacture of semiconductor devices.
Accordingly, this invention provides a method for the selective removal of trace quantities of hydride impurities that may be present in bulk or matrix hydride, inert, and non-reactive gases in parts-per-million (ppm) to parts-per-billion (ppb) levels to provide purified hydride, inert, or non-reactive matrix gases that contain less than about a 1 ppb impurity level of the unwanted hydrides. In particular, this invention provides a method for the selective and effective removal of trace levels of impurities such as germane (GeH4), silane (SiH4), hydrogen sulfide (H2S), carbon dioxide (CO2), siloxanes, phosphorus oxides (PxOy) and phosphorus oxy-acids (HxPyOz), wherein x, y, and z are small integers, from bulk or matrix hydride gases such as ammonia (NH3), phosphine (PH3) and arsine (AsH3) and from inert or non-reactive gases such as nitrogen (N2), hydrogen (H2), argon (Ar), and helium (He). In addition, and concurrently therewith, the method of this invention effectively removes trace quantities of unwanted moisture that may be within such bulk or matrix gases.
More specifically, one embodiment of this invention provides a method for removing trace levels of impurities from hydride, inert, and non-reactive gases by flowing the contaminated gas through an alumina material selected from the group consisting of an organic alumina material, a modified organic alumina material, or a modified inorganic alumina material, wherein the above-described alumina materials are thermally activated prior to use by heating under an inert atmosphere at a temperature between about 200-1000xc2x0 C. for a sufficient time and maintaining the thermally activated material in an inert atmosphere prior to use. The thermally activated modified organic or modified inorganic alumina materials are prepared by treating an unmodified organic or unmodified inorganic alumina with a modifying agent such as a basic metal salt or metal hydroxide, followed by thermally activating the modified organic or modified inorganic alumina material at a temperature between about 200-1000xc2x0 C.
This invention further provides alumina-based gas purifier materials for the selective removal of trace amounts of impurities such as germane (GeH4), silane (SiH4), hydrogen sulfide (H2S), carbon dioxide (CO2), siloxanes, phosphorus oxides (PxOy) and phosphorus oxy-acids (HxPyOz), wherein x, y, and z are small integers, and for the removal of trace amounts of moisture from hydride, inert, and non-reactive gases.
This invention further provides a method for preparing modified alumina-based gas purifier materials for the selective removal of trace amounts of impurities and for the removal of moisture from bulk or matrix hydride and inert or non-reactive gases.
Additional novel features and advantages of this invention shall be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following specification or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities, combinations, and methods particularly pointed out in the appended claims.